Chemical development of light-sensitive lead compositions

ABSTRACT

A PROCESS FOR RECORDING INFORMATION IS DESCRIBED WHICH COMPRISES INFORMATION-WISE EXPOSING TO ACTIVE RADIATION A PHOTOSENSTIVE RECORDING MATERIAL CONTAINING A PHOTOSENSITIVE LEAD COMPOUND AND DEVELOPING THE LATENT IMAGE FORMED BY MEANS OF A SODIUM DITHIONITE COMPOSITION IN THE PRESENCE OF A DIQUATERNARY CYCLIC AMMONIUM SALT WHICH BY THE UPTAKE OF 1 ELECTRON FORMS STABLE WEITZRADICALS. BY THE PRESENCE OF THE AMMONIUM SALT SELECTIVE DEVELOPMENT IS POSSIBLE IN A SHORT TIME, AT NORMAL ROOM TEMPERATUR AND NORMAL PH-VALUES.

United States Patent 3,676,131 CHEMICAL DEVELOPMENT OF LIGHT- SENSITIVE LEAD COMPOSITIONS Jozef Frans Willems, Wilrijk, Frans Clement Heugebaert, Konticlr, and Eric Maria Brinckman, Mortsel, Belgium, assiguors to Agfa-Gevaert, Mortsel, Belgium No Drawing. Filed Aug. 24, 1970, Ser. No. 66,589 Int. Cl. G03c 5/24, 1/00 U.S. Cl. 96-48 7 Claims ABSTRACT OF THE DISCLOSURE A process for recording information is described which comprises information-wise exposing to active radiation a photosensitive recording material containing a photosensitive lead compound and developing the latent image formed by means of a sodium dithionite composition in the presence of a diquaternary cyclic ammonium salt which by the uptake of l electron forms stable Weitzradicals. By the presence of the ammonium salt selective development is possible in a short time, at normal room temperature and normal pH-values.

The present invention relates to the chemical development of photographic materials of the non-silver halide type.

The formation and development of latent silver images is generally known. The replacement of silver by other metals has been made the object of an intensive research in order to lower the cost of the photographic materials.

Among the photosensitive metal compounds other than silver halide, inorganic photosensitive lead compounds for example lead (II) oxide and lead (II) halides such as lead iodide, and lead bromide can be mentioned.

Photosensitive lead compounds, owing to their electrochemical potential, cannot be chemically developed by the classical organic reducing agents used for the development of exposed silver halide emulsions. In order to chemically develop lead compound emulsions strong reducing agents are required such as sodium dithionite, sodium arsenite, tin (II) compounds such as the tin (II) chelate of ethylene diamine tetraacetic acid, etc. Development by means of these strong reducing agents, however, give no satisfying results in that at normal room temperature and acceptable pH-values these agents develop the lead compound emulsions very slowly and with poor selectivity. At increased temperature, say from 40 to 50 0, development is somewhat accelerated but at these temperatures the layers detach easily.

It has now been found that exposed emulsions of photosensitive inorganic lead compounds can be successfully developed in a short time, at normal room temperature and normal pH-value e.g. using borax, by means of sodium dithionite as reducing agent when carrying out said development in the presence of diquaternary cyclic ammonium salts which by the uptake of 1 electron form stable Weitz-radicals, whether as an additive to the emulsion or to the developing bath.

Particularly suitable ammonium salts of use according to the present invention are the dipyridinium, dithiazolium, diimidazolium salts as well as the pyridinium-thiazolium and pyridinium-imidazolium salts corresponding to the following general formula:

"ice

wherein each of Z and Z (the same or different) stands for the atoms necessary to close a pyridinium, thiazolium or imidazolium nucleus which may carry fused-on aryl nuclei such as benzothiazolium, benzoimidazolium and quinolinium and which may be further substituted for example by alkyl and aryl,

A stands for a chemical bond linking the 2-position of 2 pyridinium, thiazolium or imidazolium to the 2-position of Z =pyridinium, thiazolium or imidazolium or to the 4-position of Z =pyridinium or for a chemical bond linking the 4-positions of Z =Z ==pyridinium,

each of R and R stands for alkyl including substituted alkyl, or R together with R may stand for ethylene including substituted ethylene when A is a chemical bond linking the 2-position of Z, to the 2-position of Z and X- stands for an anion or acid radical such as halide, p-

toluene sulphonate, alkyl sulphate and perchlorate.

Representative examples of compounds corresponding to the above general formula are:

Compounds 1 and 2 are commercially available compounds marketed in the form of 39% and 20% aqueous solutions respectively under the trade names Reglone and Gramoxone by Imperial Chemical Industries, Ltd., London, England.

Compounds 3-6 can be prepared as is illustrated by the following preparations.

PREPARATION 1: COMPOUND 3 21.2 g. (0.1 mole) of 2-(4-pyridyl)benzothiazole and 250 g. (2 mole) of dimethyl sulphate are heated for hours at 110 C. on an oil bath. The precipitate formed upon cooling is filtered by suction and washed with diethyl ether. Yield: 40 g. Melting point: 190 C.

PREPARATION 2: COMPOUND 4 5 g. (0.025 mole) of 1,10-phenanthroline monohydrate and 20 m1. of dibromoethane are refluxed for 11 h. whereupon the precipitate formed is recrystallized from ethanol/ water. Yield: 3 g. Melting point: 260" C.

PREPARATION 3: COM-POUND 5 6.8 g. (0.025 mole) of 1-pheny1-2-(2-pyridyl)benzoimidazole and 20 ml. of dibromoethane are refluxed for 1 hr. whereupon the precipitate formed is recrystallized from ethanol. Yield: 5 g. Melting point: 260 C.

PREPARATION 4: COMPOUND 6 10.6 g. (0.05 mole) of 2-(2-pyridyl)benzothiazole and 9.4 g. (0.05 mole) of dibromoethane are heated for 48 hours at 130 C. in a sealed tube whereupon the residue is boiled with acetone. Yield: 4 g. Melting point: 260 C.

Thus, in accordance with the present invention a process is provided for recording information comprising the steps of information-wise exposing to active radiation a photo-sensitive recording material comprising a photosensitive lead compound such as lead (II) oxide, lead bromide, lead iodide or a crystalline mixture of lead bromide and lead iodide and developing the thus formed latent image in a solution comprising sodium dithionite, in the presence of a diquaternary cyclic ammonium salt as defined above.

The invention further provides a photosensitive recording material comprising a photo-sensitive lead compound in conjunction with a diquaternary cyclic ammonium salt as defined above.

The development accelerating diquaternary cyclic ammonium compounds of use according to the present invention may be added to the developer or to the lead compound emulsion or to both simultaneously.

The compounds of use according to the invention can be added to the photosensitive lead compound emulsions preferably in dissolved form in water or a mixture of water and water-miscible organic solvents. However, they can also be incorporated into the said emulsions by imbibition by treating them with a solution containing these compounds or by diffusion from adjacent water-permeable layers comprising these compounds.

The amount of diquaternary cyclic ammonium compound added to the emulsion or to the developer can vary within wide limits. The optimum concentration for any compound can best be determined by employing a series of concentrations in several batches of the same emulsion or developer and determining the speed obtained before and after incorporation of the said compound. Usually, the compounds of use according to the present invention are used in'amounts ranging between 10 mg. and 1 g. per mole of lead compound when used in the emulsion and between 10 mg. and g. per liter when used in the developer.

Materials making up the continuous phase of the photosensitive layer used in the present invention are hydrophilic binding agents or binding agent systems, e.g. hydrophilic natural colloids, modified hydrophilic natural colloids, or synthetic hydrophilic polymers.

More particularly they may be selected from such filmforming natural or modified natural hydrophilic colloids, which are water-permeable and do not adversely effect the photographic properties of the photosensitive lead compounds, e.g. gelatin, glue, casein, zein, hydroxyethylcellulose, carboxymethylcellulose, gum arabic, sodium alginate and hydrophilic derivatives of such colloids. They may also be selected from such synthetic hydrophilic polymers as, e.g., polyvinyl alcohol, poly(N-vinylpyrrolidone), polyvinylamine, polyethylene oxide, poly(styrene sulphonic acid), polyacrylic acid, polyacrylamide, and hydrophilic copolymers and derivatives of such polymers. In preparing a recording layer according to the present invention gelatin is used preferably.

The hydrophilic binder material used in the photosensitive surface layer is preferably hardened to some extent to obtain a layer with higher mechanical strength. Thus, e.g. a hydrophilic binding agent of the gelatin type may be hardened by reaction with an aldehyde such as formaldehyde or glyoxal. The hardening agents may be incorporated into the coating composition or they may be incorporated into the coated layer by imbibition. The use of latent hardening agents, from which e.g. the hardening agent is generated by heating, is not excluded.

Both the amount and the type of hardening agent chosen depend on the mechanical strength desired. When using gelatin the amount of hardening agent may be in the range of 0.5 to 5% by weight in respect to the gelatin. The hardening of the recording layer may be effected with a solution containing the hardening agent e.g. formaldehyde in an amount of 0.5 to 25% by weight.

The flexibility of the recording layer may be improved by means of plasticizing agents known in the art, e.g. latices, phosphonic or phosphoric acid esters of polyols and/ or monoalkylene glycol alkyl ethers and/ or polyoxyal'kylene glycol monoalkyl ethers.

As photosensitive lead compounds preferably lead (II) oxide, lead (II) iodide and lead (II) bromide or mixtures of the latter two e.g. crystalline mixtures thereof, are used.

The lead halides may be freshly prepared in finely divided state occasionally in the presence of the binding agent(s) e.g. by a reaction of a dissolved water-soluble lead compound e.g. lead acetate, with sodium iodide or sodium bromide.

Two types of lead (II) oxide exist viz the commercially available lead (11) oxide, which is a yellow pigment having an orthorhombic crystalline structure, also called massicot, and the red to tan lead (II) oxide, which possesses a tetragonal crystalline structure, also called litharge. The large crystals of the latter are carmine red and the small are tan.

The lead (II) oxide for use in accordance with the present invention preferably consists of lead (H) oxide of the yellow type. However, doped yellow lead (II) oxide and mixtures of yellow and red lead (II) oxide are not excluded and useful results can still be obtained with a lead (II) oxide mixture consisting of 75% by weight of red lead (11) oxide and 25% by weight of yellow lead (II) oxide.

The grain size of the photo-sensitive lead compounds is preferably between 0.03 and about 10 microns. The ratio by weight of binding agent to photo-sensitive lead compound is preferably between 9:1 and 1:3. The amount of photo-sensitive lead compound per sq. m. can vary within wide limits but preferably amounts to at least 1 g. per

sq. m.

The photo-sensitive lead compound emulsion layer of a photo-sensitive recording material of use according to the present invention can be sensitized by means of so-called chemical sensitizers, amongst which sulphur compounds or compounds wherein sulphur has been replaced by selenium or tellurium. Examples of suitable chemical sensitizers can be found in the US. Pat. 2,414,839 and in Belgian Pats. Nos. 741,538 and 741,539. The photo-sensitive lead compounds may be treated with the chemical sensitizers before, during or after being applied to the support. Preferably, they are added to the coating composition before coating.

The lead compounds are inherently sensitive to electromagnetic radiation, which is rich in ultra-violet rays.

The photo-sensitive lead compounds may be spectrally sensitized and for that purpose dyes may be used that are known for increasing the spectral sensitivity of photosensitive silver halide.

By dye sensitization the said lead compounds can be made more sensitive to light of the visible spectral region, so that they can yield a developable latent image by exposure with light emitted by a tungsten filament lamp or a dash lamp mainly emitting in the visible spectrum.

The recording material may be exposed in dry or wet state for example the recording material may be exposed immediately after it has been dipped into an aqueous solution containing chemical sensitizers.

In order to improve the wetting of the recording layer it preferably contains a Wetting agent or water-attracting compound such as glycerol or water-attracting salts and hydratable metal oxides.

The support of the recording material securing sufficient mechanical strength to the material may be a paper support, a metal sheet or a synthetic film support that may be transparent such as polyethylene terephthalate and cellulose triacetate.

The recording layer must strongly adhere to the support for not getting loose therefrom during its treatment. If necessary, one or more appropriate subbing layers are applied between the support and the recording layer.

A latent image produced on a recording material according to the present invention is chemically developed by means of sodium dithionite or addition products thereof with formaldehyde such as Rongal HT type 66 (trade name of Badische Anilin- & Soda-Fabrik, Ludwigshafen, Germany), whereby lead metal provided by the photosensitive lead compounds forms the visible image.

The sodium dithionite may be used in conjunction with a complexing agent for lead salts e.g. ethylene diamine tetraacetic acid applied in alkaline medium.

The lead image may be stabilized against moisture by treating the developed material with a solution of a soluble ionized chloride, e.g. sodium chloride or cadmium chloride.

The following examples illustrate the present invention.

EXAMPLE 1 2 g. of Cyanamer P 250 (trade name of the American Cyanamid Company, Bound Brook, N.J., U.S.A. for a polyacrylamide of which a 2% aqueous solution has a Brookfield viscosity at 25 C. of 2000) and 2 g. of gelatin were dissolved at 45 C. in 100 ml. of water. To the solution obtained were added with stirring by means of a high speed stirrer:

0.005 N solution of compound 1 ml 4 Finely ground lead bromide g 16 prepared by admixture with strong stirring of an equivalent amount of lear acetate with an equivalent amount of sodium bromide both in aqueous solution, whereupon the precipitate of lead bromide was filtered off, washed with distilled water and dried;

Glycerol g-.. 3 12.5% aqueous solution of saponin ml 0.5 4% aqueous solution of formaldehyde ml 0.5

The photo-sensitive lead bromide emulsion formed was coated onto a subbed polyethylene terephthalate support pro rata of about 100 g./sq. in.

After drying, the material was exposed for 20 sec. through a transparent negative by means of a conven- 6 tional rotary office copying machine as employed for making diffusion transfer copies.

The latent image formed was then developed at 20 C. by means of a bath having the following composition:

Borax l0 Rongal HT type 66 (trade name) 25 Water to make 1 litre.

The maximum density of the image obtained was 0.9 after a development time of 2 min.

A material prepared as described above but comprising no compound 1 could also be developed at 20 C. by means of sodium dithionite provided sodium hydroxide was added to obtain a pH of 14 and even then development occurred markedly slower than when the material comprised compound 1. When increasing the developing temperature to 60 C. development was accelerated but the emulsion layer detached from the support.

EXAMPLE 2 EXAMPLE 3 20 g. of yellow lead (II) oxide comprising 20 ppm. of bismuth were ball-milled for 1 hour in 50 g. of demineralized water. To the suspension obtained the following solution was added at 35 C. with stirring:

G. 10% solution of gelatin in demineralized water 50 Glycerol 4 12.5 solution of saponin in demineralized water 1 The suspension formed was coated on a subbed cellulose triacetate support in such a way that after drying the photo-sensitive layer had a thickness of 21 microns.

The material was exposed image-wise through a grey filter having an overall density of 1.00 in a Buroza 600 diazoprint apparatus (trade name of De Atlas, Delft, Netherlands, for a diazoprint apparatus) at a travelling speed of 2 cm./ sec.

The exposed material on which only a faint print-out image could be observed was then dipped in the following successive baths A, B and C.

(A) 60 seconds in a developing bath of the following composition:

Rongal HT type 66 (tradename) g 5 30% solution of compound 1 in demineralized water ..ml.. 2

Demineralized water to make ml.

(B) 30 seconds in 20% solution of sodium thiosulphate- 5-water in demineralized water.

(C) 30 seconds in a 10% solution of glacial acetic acid in demineralized water.

After rinsing and drying a black image was obtained having a maximum density of 0.82 and a minimum density of 0.32, the densities having been measured by reflected light.

When compound 1 was omitted from the developing bath no image was visible at the end of the processing cycle.

We claim:

1. Process for recording information comprising the steps of information-wise exposing to active radiation a photo-sensitive recording material comprising a photosensitive lead oxide or lead halide and developing the thus formed latent image by means of an aqueous sodium dithionite solution in the presence of a diquaternary cyclic ammonium salt which by the uptake of 1 electron forms stable Weitz-radicals.

2. Process according to claim 1, wherein said diquaternary cyclic ammonium salt corresponds to the formula:

each of Z and Z stands for the atoms necessary to close a pyridinium, thiazolium or imidazolium nucleus which may carry fused-on aryl nuclei,

A stands for a chemical bond linking the 2-position of Z =pyridinium, thiazolium or imidazolium to the 2- position of 2: =pyriminium, thiazolium or imidazolium or to the 4-position of Z =pyridinium or for a chemical bond linking the 4-positions of Z ==Z =pyridinium,

each of R and R stands for an alkyl group or R together with R may stand for ethylene including substituted ethylene when A is a chemical bond linking the 2-position of Z to the 2-position of 2;, and

X- stands for an anion.

3. Process according to claim 1, wherein the diquaternary cyclic ammonium salt is present in the recording material in an amount comprised between mg. and 1 g. per mole of lead compound.

4. Process according to claim 1, wherein the diquaternary cyclic ammonium salt is present in the sodium dithionite composition in an amount comprised between 50 mg. and 5 g. per litre.

5. A photo-sensitive recording material comprising a photo-sensitive lead oxide or lead halide and a diquaternary cyclic ammonium salt which by the uptake of 1 electron forms stable Weitz radicals.

6. A photo-sensitive recording material according to claim 5, wherein said diquaternary cyclic ammonium salt corresponds to the formula:

each of Z and Z stands for the atoms necessary to close a pyridinium, thiazolium or imidazolium nucleus which may carry fused-on aryl nuclei,

A stands for a chemical bond linking the 2-position of Z =pyridinium, thiazolium or imidazolium to the 2- position of Z ==pyridinium, thiazolium or imidazolium or to the 4-position of Z =pyridinium or for a chemical bond linking the 4-p0sitions of Z =Z pyridinium,

each of R and R stands for an alkyl group, or R together with R may stand for ethylene including substituted ethylene when A is a chemical bond linking the 2-position of Z to the 2-position of Z and X- stands for an anion.

7. A photo-sensitive recording material according to claim 5, wherein said salt is present in an amount comprised between 10 mg. and l g. per mole of lead compound.

References Cited FOREIGN PATENTS 1,086,384 1967 Great Britain 9688.

NORMAN G. TORCHIN, Primary Examiner R. E. FIGHTER, Assistant Examiner U.S. Cl. X.R. 96-88 UNITED STATES PATENT. OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 676, 131 Dated July 11, 1972 Inventor(s) JOZEF FRANS WILLEMS ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, in the heading, "Agfa-Gevaert" should read .Agfa- Gevaert, N. V. Column 1, in the heading, insert the priority claim as follows:

Claims priority, application Great Britain, Oct. 27, 1969, 52, 570/69 Column 2, lines 40-48, formula 4, the formula should appear as follows:

a 1 1 I I I ('2; I

Column 5, line 40, "Germany should read W-Germany Column 5, line 62, 'lear" should read lead Column 7, line 20, claim 2, "Z: =pyriminium" should read Z =pyridinium Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attosting Officer Commissioner of Patente FORM PO-105O (10-69) USCOMM-DC 6Q376-P6Q 9 U5. GOVERNMENT PRINYING OFFICE: I989 0-366-334. 

